1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to methods of determining ion implant dose.
2. Description of the Related Art
Ion implantation is a widely used technique in the fabrication of integrated circuits on semiconductor wafers. Owing to its delivery of faster throughput and more precise placement of dopants, ion implantation has supplanted chemical diffusion in many applications as the preferred method of introducing impurities into films and structures on a semiconductor wafer.
In a general sense, ion implantation involves the placement of a semiconductor wafer in an ion implantation tool where an energetic beam of charged atoms or molecules is directed toward specified locations on the wafer. The implant may be performed across the entire wafer surface non-selectively. More commonly though, the implantation of the ionic species is restricted to certain portions of the substrate. To this end, appropriate masking is applied to the wafer surface prior to the implant.
Ion implanters are among the most complex systems used in the fabrication of integrated circuits on semiconductor wafers. Most conventional ion implanters include an ion source, an i on extraction and analyzing device of some sort, an acceleration tube, and a high vacuum system. The complex choreography for these various systems necessary for successful ion implantation is normally handled by a computer control system, which is designed to automate as many of the phases of the implantation process as possible. The control system is normally tasked with monitoring a large number of parameters to ensure that the implantation proceeds normally.
Despite the wide spread usage of complex control systems and finely tuned ion implanter subsystems, ion implantation processes do not always proceed normally. In many cases, the implant is interrupted or otherwise aborted prior to completion. The reasons for such aborts are legion and include unacceptable deviations in beam current, chamber pressure, beam composition and voltage variations to name just a few.
Characterization of ion implantations must be performed in order to verify implant dose, implant depth profiles and uniformity of implant dose across the surface of the wafer. Accurate post implant characterization is particularly important in circumstances where the implant experiences an abort. In such cases it is vital to determine the dose delivered to the wafer so that the need and specifications for a make-up implant can be determined.
One conventional technique for characterizing partially implanted wafers involves thermal wave analysis. However, thermal wave analysis may not yield an exact dosage. This is because the analysis is based on a plasma wave by laser excitation and does not have a linear relationship between the thermal wave and the implant dose. It is also dependent on the energy and species of implant. Furthermore, thermal wave measurement is of very limited benefit for analyzing implanted substrates that have undergone pre-amorphization implants. Such pre-amorphization implants are common techniques used to condition a substrate in order to establish shallow impurity junctions post implant.
Another conventional technique for characterizing ion implants is secondary ion mass spectrometry (xe2x80x9cSIMSxe2x80x9d). In conventional SIMS analysis, a small sample of the wafer is clipped is subjected to ion beam sputtering. This technique is destructive when performed on active circuit structures. If performed on a masked structure, the technique may still be destructive and may not provide sufficient sensitivity since the width of the sputtering beam is normally one or more orders of magnitude larger than the widths of mask openings.
Another conventional technique involves the use of x-rays as both the primary scanning beam and the detected entity. However, conventional x-ray fluorescence utilizes a relatively large diameter beam which restricts its use on small features integrated circuits. Furthermore, the penetration of the primary x-ray beam can cause spurious emissions due to surface roughness and depth sensitivity of the detected x-ray signals.
The various limitations of the conventional characterization techniques often translate into the destructive testing of production wafers that may have already undergone substantial processing. Such wafers usually must be scrapped. For those non-destructive techniques, there may be significant limitations with regard to the accuracy of the characterization.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a method of processing a semiconductor workpiece that has a device region and an inactive region is provided. A first mask is formed on a first portion of the inactive region. A first implant of ions is performed on the device region and the first mask. A secondary ion mass spectrometry analysis of the first portion of the first mask is performed to determine a composition thereof relative to a standard composition. A dose for the first implant is determined based upon the secondary ion mass spectrometry analysis of the first portion of the first mask. The first implant dose is compared with a prescribed dose for the first implant to determine if a second implant is necessary to achieve the prescribed dose, and if so, an appropriate make-up dose for the second implant.
In accordance with another aspect of the present invention, a method of processing a semiconductor workpiece that has an inactive region and a device region with at least one integrated circuit is provided. A first mask is formed on a first portion of the inactive region. A first implant of ions is performed on the least one integrated circuit and the first mask. The existence of an interruption in the first implant is determined. If an interruption in the first implant is detected, a secondary ion mass spectrometry analysis of the first portion of the first mask is performed in order to determine a composition of the first mask relative to a standard composition. A dose for the first implant is determined based upon the secondary ion mass spectrometry analysis of the first portion of the first mask. The first implant dose is compared with a prescribed dose for the first implant to determine if a second implant is necessary to achieve the prescribed dose, and if so, an appropriate make-up dose for the second implant.
In accordance with another aspect of the present invention, a method of processing a semiconductor workpiece that has an inactive region and a device region with at least one integrated circuit is provided. A first mask is formed on a first portion of the inactive region. A first implant of conductivity-altering impurity ions is performed on the at least one integrated circuit and the first mask. The existence of an interruption in the first implant is determined. If an interruption of the first implant is detected, a secondary ion mass spectrometry analysis of the first portion of the first mask is performed in order to determine a depth profile of the conductivity-altering impurity ions relative to a standard depth profile. A dose for the first implant is determined based upon the secondary ion mass spectrometry analysis of the first portion of the first mask. The implant dose is compared with a prescribed dose for the first implant to determine if a second implant is necessary to achieve the prescribed dose, and if so, an appropriate make-up dose for the second implant.
In accordance with another aspect of the present invention, a method of processing a semiconductor workpiece that has a device region and an inactive region is provided. A first mask is formed on a first portion of the inactive region. A first implant of ions is performed on the device region and the first mask. A secondary ion mass spectrometry analysis of the first portion of the first mask is performed to determine a composition thereof relative to a standard composition. A dose for the first implant based upon the secondary ion mass spectrometry analysis of the first portion of the first mask is determined.